In electrophotography, generally photoconductive materials including selenium are used as a photoreceptor and an electrical latent image is formed by various methods. The latent image is developed with toner which adheres to the latent image. In this developing process, a toner-carrying particle known as "carrier" is used to impart an appropriate quantity of positive or negative triboelectrification to the toner.
In general, a carrier is classified as coated or non-coated, with a coated carrier having superior life when used in the developing process.
Among the different carrier coating materials, a fluoro-type resin can retard toner filming and has excellent resistance to surface contamination because of its low surface energy. However, its adherence to magnetic particles is unsatisfactory, making it difficult to form a continuous and complete coating layer on the carrier which resists damage.
As a result of the unsatisfactory coating, after extended use, changes occur in the carrier's triboelectrification level and its sensitivity to temperature and humidity, causing the premature formation of fog and contamination in the inside of the machine.